What are the reasons for the failure of the injection mold(2)


4. The movable template is bent. When the mold is injec […]

4. The movable template is bent. When the mold is injected, the molten plastic in the mold cavity generates a huge back pressure, which is generally 600 ~ 1000 kg / cm2. The mold maker sometimes does not pay attention to this problem, often changes the original design size, or replaces the movable template with a low-strength steel plate. In the mold that uses ejector pins, the template has a large span between the two sides, which causes the template to bend down during injection. Therefore, the moving formwork must be made of high-quality steel, and it must have a sufficient thickness. Low-strength steel plates such as A3 must not be used. When necessary, support columns or blocks should be set under the moving formwork to reduce the thickness of the formwork and improve the carrying capacity.

5. The ejector pin is bent, broken or leaking. The quality of the self-made ejector is better, which means that the processing cost is too high. Nowadays, standard parts are generally used, and the quality is poor. If the gap between the ejector pin and the hole is too large, material leakage will occur, but if the clearance is too small, the ejector pin will swell due to the rise of the mold temperature during injection. What is more dangerous is that sometimes the ejector rod is ejected at a normal distance, and then it breaks. As a result, the exposed ejector rod cannot be reset when the next mold is closed, and the concave mold is damaged. In order to solve this problem, the ejector rod was reground, and a fitting section of 10 to 15 mm was retained at the front end of the ejector rod, and the middle part was ground 0.2 mm smaller. After assembly of all ejectors, the fit clearance must be checked strictly, generally within 0.05 ~ 0.08 mm, to ensure that the entire ejection mechanism can move forward and backward freely.

6. Poor cooling or leaking water. The cooling effect of the mold directly affects the quality and production efficiency of the product, such as defects such as poor cooling, large shrinkage of the product, or uneven shrinkage and deformation of the warped surface. On the other hand, the mold is overheated in whole or in part, which makes the mold unable to be molded normally and stop production. In severe cases, the movable parts such as the ejector pin are thermally expanded and stuck and damaged. The design and processing of the cooling system are determined by the shape of the product. Do not omit this system because of the complex mold structure or processing difficulties, especially the large and medium-sized molds must fully consider the cooling problem.